Corrosion is the electrochemical reaction of metal with its environment. It is a destructive reaction which, simply stated, is the reversion of refined metals to their natural state. For example, iron ore is iron oxide. Iron oxide is refined into steel. When steel corrodes, it forms iron oxide which may result in failure or destruction of the metal causing a system to be shut down until necessary repairs can be made.
When crude oil and natural gas are removed from a formation they frequently contain CO.sub.2 or H.sub.2 S (acid gases). Acid gases are commonly removed from the hydrocarbon in an acid gas removal amine system (amine unit). An amine unit utilizes an alkanolamine such as monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA), diisopropylamine (DIPA), diglycolamine (DGA), or triethanolamine (TEA) diluted in water as an amine solvent. The hydrocarbon containing acid gases are contacted with the amine solvent in a tray or packed absorber where the amine solvent reacts with the acid gases thereby removing them from the hydrocarbon. The amine-acid gas reaction is later reversed in a plate or packed stripper resulting in an acid gas stream and a reusable amine solvent.
Amine units present a variety of corrosion control problems. Unreacted carbon dioxide dissolved in the aqueous alkanol amine solvent forms acid species which are corrosive to metals. Oxygen can enter an amine unit through storage tanks, sumps, surge vessels, and the like and attack metals causing corrosion. Oxygen also can oxidize the alkanolamine. Oxidation products of alkanolamines cause metal corrosion. Efforts to control corrosion in amine units usually focus on the use of metallurgy, minimization of acid gas flashing, filtration, stress relieving, process controls and chemical corrosion inhibitors. These measures help reduce corrosion in amine units but do not eliminate the problem. Since corrosion if left untreated, can cause shut-down of an amine unit, corrosion control is a very important consideration.
Accordingly, a need exists for compositions which when added to an aqueous alkanolamine solution in an acid gas removal amine unit inhibits CO.sub.2 and O.sub.2 induced corrosion of ferrous metals in contact with the aqueous alkanolamine solutions.